Conventional vehicles until around 1960 were lightweight and did not required to have high cruising speed, and so bias tires of low load and narrow sectional width were used. Currently, wider radial tires have been increasingly developed for heavier and faster vehicles (for example, JP H7-40706 A (PTL 1)).
Wider tires, however, strain the vehicle space and lower the vehicle ride comfort. Besides, an increase in air resistance causes lower fuel efficiency.
Growing concern about environmental issues in recent years has enhanced the demand for high fuel efficiency. High fuel efficiency can be assessed based on rolling resistance (RR). Lower rolling resistance is known to contribute to higher fuel efficiency.
It is known that increasing the diameter and width of a tire is effective in reducing the rolling resistance coefficient (RRC) of the tire to achieve higher fuel efficiency. However, when the tire is increased in diameter and width, the tire weight and the air resistance increase. This causes higher vehicle resistance and makes it impossible to achieve sufficient rolling resistance reduction effect, and also leads to excessive load capacity of the tire.
In view of this problem, we have proposed a technique of a passenger vehicle pneumatic radial tire of narrow width (narrow tire width) and large diameter (large tire outer diameter) in which the internal pressure, sectional width (SW), and outer diameter (OD) of the tire satisfy a specific relationship (for example, WO 2012/176476 A1 (PTL 2)).